1. Field of the Invention
The present invention relates to a fuel injection nozzle for a diesel engine. More particularly, the invention is directed to a fuel injection nozzle having a needle valve.
2. Background of the Invention
A fuel injection nozzle of a diesel engine, especially a direct-injection type engine, generally has a needle valve inserted in a nozzle body having a plurality of nozzle holes. When fuel is introduced to a fuel inlet passage formed within the nozzle body, the needle valve is lifted by fuel pressure so that the fuel passes through a gap formed between a surrounding wall of the needle valve and an inner wall of the nozzle body. The fuel is then injected through the plurality of nozzle holes into a combustion chamber (piston cavity) of the engine.
The opening area of each nozzle hole, in the conventional diesel engine fuel injection nozzle, is fixed. When the fuel pressure is high, i.e., in a high-load state, sufficiently high spray penetration can be attained. However, when the fuel pressure is low, i.e., in a low-load state, the spray penetration is reduced, and the fuel will not be sufficiently atomized. Therefore, the fuel will be combusted before it is sufficiently mixed with air. This causes longer ignition delay, increases combustion noise, deteriorates exhaust emission performance, and causes smoke problems.
A rotary valve having a fuel passage is known to be used for throttling fuel through the nozzle. The rotary valve is rotated by a pulse motor or the like. During the low-load state, a nozzle hole area is throttled, and spray penetration of the fuel is increased. However, a pulse motor increases the size of the fuel injector assembly and its manufacturing cost. Furthermore, the structure of the injector assembly becomes complex, decreasing the reliability of the injector assembly.
The present invention is directed to solving the above-mentioned problems of the conventional fuel injection nozzle by attaining good combustion performance and good exhaust emission performance. Moreover, the present invention is also directed to achieving such performance by a fuel injection nozzle having a simple structure without increasing the size of the injector assembly. Also, the present invention may reduce the size of the piston cavity, thereby enabling reduction of the engine size as a whole by effectively utilizing the spray penetration to mix the fuel with the air.
In accordance with the invention, a fuel injection nozzle is provided for a diesel engine. The fuel injection nozzle includes a nozzle body having a tip end portion, a top end portion having an opening edge, and a fuel inlet passage, the tip end portion having a plurality of first nozzle holes. The nozzle body has a first protrusion formed on a peripheral wall adjacent to the opening edge, and the first protrusion protrudes from an inner peripheral surface toward a center axis of the nozzle body. The fuel injection nozzle also includes a needle valve inserted in the nozzle body. The needle valve has a tip end portion, a top end portion, a first guide groove formed on an outer peripheral surface at the top end portion of the needle valve and inclining in a direction with respect to an axial direction of the needle valve, and a second guide groove formed on an outer peripheral surface of the tip portion of the needle valve and inclining in an opposite direction to the first guide groove with respect to the axial direction. The tip end portion has a gap with respect to the tip portion of the nozzle body, and the first guide groove is engaged with the first protrusion allowing the needle valve to axially rotate corresponding to a movement of the needle valve in the axial direction. The fuel injection nozzle includes a bag-shaped rotary valve fitted with the tip end portion of the needle valve. The rotary valve has a second protrusion protruding toward the center axis and being engaged with the second guide groove. The rotary valve has a plurality of second nozzle holes configured to have an overlapping area with the plurality of first nozzle holes. The overlapping area increases as the rotary valve rotates due to the movement of the needle valve in the axial direction.
In another aspect, a fuel injection nozzle of a diesel engine is provided with a first serration formed on an inner peripheral surface of a guide ring fitted to a groove formed on the opening edge of the nozzle body. The guide ring is prohibited from rotation, and the first serration inclines with respect to the axial direction. The nozzle also includes a second serration formed on an outer peripheral surface at the top end portion of the needle valve. The second serration is engaged with the first serration allowing the needle valve to rotate corresponding to movement of the needle valve in the axial direction. A tip portion on a nozzle hole side of the needle valve has a gap with respect to an inner surface of a tip portion on the nozzle hole side of the nozzle body. The tip portion of the nozzle hole side of the nozzle valve is fitted with a bag-shaped rotary valve. A third serration and a fourth serration are formed on an outer peripheral surface at the tip portion of the needle valve and on an inner peripheral surface of the rotary valve, respectively. The third serration and the fourth serration are engaged with each other with a gap therebetween and incline in a direction opposite to the first and second serrations with respect to the axial direction. A plurality of second nozzle holes are formed such that an overlapping area of the plurality of second nozzle holes with the plurality of first nozzle holes formed in the nozzle body increases the lifting of the needle valve in the axial direction.
In yet another aspect, a fuel injection nozzle for a diesel engine includes a nozzle body having a tip end portion, a top end portion having an opening edge, and a fuel inlet passage. The tip end portion has first nozzle holes. A guide ring is fitted at the opening edge and has a first serration substantially inclined with respect to an axial direction. A needle valve is inserted in the nozzle body and has a tip end portion, a top end portion, a second serration formed at the top end portion thereof, and a third serration at the tip end portion thereof. The second serration is engaged with the first serration. The first and second serrations allow the needle valve to rotate and move in the axial direction creating a first gap between the nozzle body and the needle valve when fuel is introduced through the fuel inlet passage. A rotary valve is disposed between the tip end potion of the needle valve and the tip end portion of the nozzle body. The rotary valve has second nozzle holes in the tip end portion thereof and a fourth serration. The second nozzle holes are configured to have an overlapping area with the first nozzle holes, and the overlapping area increases as the needle valve is lifted in the axial direction. The fourth serration is engaged with the third serration with a second gap therebetween and is inclined in a direction opposite to the first and second serrations with respect to the axial direction.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.